1. Field of the Invention
This invention relates to lampholders for lamps having a sealing surface between the holder and the lamp, surrounding the electrical connection portion, and more particularly to lampholders for in-line fluorescent lamps held under axial pressure between two holders.
2. Description of the Prior Art
Electric lamps used in outdoor locations or other places exposed to high humidity, or to vapors having conducting or corrosive properties, require sealing of the space in which the lamp terminals make electrical connection with the contact fingers or surfaces of the lamp socket if long, reliable operation is to be obtained. Maintenance of this seal is a special problem with fluorescentlamps because of their unusually long, slim tubes having a separate connection at each end. Because of this configuration, there is a great tolerance build up between the ends so sealing is difficult.
The U.S. Pat. to G. A. Nelson, No. 3,111,353 issued Nov. 19, 1963, discloses a fluorescent lampholder having a rubber sealing ring placed in a groove in the face of a dielectric body, the ring having a surface protruding to contact and seal against the end of a tube inserted in the socket. Pressure exerted between a fixed socket at one end, and a spring-loaded plunger socket at the other, hold the sealing rings at each end in place. This design, however, had the two-fold disadvantage that the sealing rings did not always make a tight seal because of mis-alignment between the face of the dielectric and the tube end; and while attempting to insert one end of a long tube, an installer would easily dislodge the ring so that it came out of the groove and dropped un-noticed.
More recently, U.S. Pat. No. 3,384,858 issued May 21, 1968 to G. Johnson describes a lampholder having a resilient ring cemented to the front walls of the fixed lampholder and the compressible lampholder. This cementing alleviated the problem of accidental dislodging of the ring. A later filed application by Johnson resulted in issuance of U.S. Pat. No. 3,353,140 on Nov. 14, 1967, which teaches cementing the sealing ring, and further discloses the incorporation of a tilting capability in both lampholders so that mis-alignments would be compensated for. Lampholders of this general design have been in commercial use since then. However, because of the properties of the materials used, it has been found that after prolonged use, these cement grips between the sealing ring and the lampholder may become severely weakened or lost, so that the ring does not adhere to the lampholder. In fact, in some instances the ring adheres to the fluorescent lamp itself, a phenomenon believed due to migration of the hardening component used in the cement. This has the particular drawback that the installer will not notice the ring falling from the lampholder, and will be unware that the contacts will become exposed to corrosion.